Not every attempt by a mobile terminal to access a wireless communications network succeeds in establishing a connection to the network. An access attempt may not mature into a connection to the network due to an RF-related failure, as for example a weak RF signal, or a non-RF related failure, as for example a lack of base station amplifier power, the lack of an available base station, base station processing overload, the lack of transmission resources between the base station and the switch to which it is connected, or an overload condition at the switch. Thus, if the network reaches its maximum capacity to handle calls, subsequent access attempts will not result into a viable connection. Each access attempt, if the base station recognizes it, is recorded as a “seizure.” Under normal conditions, however, operating at the load the base station and switch have been designed to handle, most seizures result in what is known as an “assignment” by the base station. Under normal circumstances, a very high percentage, for example 98–99%, of seizures become assignments. It should be noted that once a call is assigned by a base station, other factors such as various network conditions and the called party's status, may preclude completion of network connection to its intended destination.
There are times, however, when the number of access attempts within a base station's coverage area may be significantly higher than the capacity of that base station or the wireless network. Such an abnormally busy period could result from a local or wide-area emergency or a time-related condition. For example, any hot activity in a localized area caused by, for example, a local emergency such as a plane crash or a massive highway accident, the ending of a highly attended football or baseball game, or the switching from more costly “day minutes” to free “night minutes” at 8:00 PM or 9:00 PM, could result in a large number of unsuccessful access attempts at a base station. This abnormally high volume of access attempts could last for a period of only several minutes or could extend for over an hour or more depending on the cause of the high level of activity. In rare emergency situations, such as in the aftermath of the World Trade Center tragedy on Sep. 11, 2001, an overload condition existed over an extended period of time. As a result of any such overload condition, the large number of almost simultaneous access attempts that is beyond the capacity for which the wireless network has been designed can have a deleterious effect on those ongoing calls that have succeeded in obtaining an assignment. Specifically, the access probes generated and transmitted on the common reverse access channel by the many mobile terminals in their unsuccessful access attempts at generally increasing power levels will create interference on the reverse link that shares the same spectrum as the reverse access channel and that is used by all the mobile terminals that have been able to obtain an assignment. As a result, the large number of access probes made at what are increasing power levels can affect the frame error rate of the ongoing voice or data calls. Furthermore, the interference created on the reverse link can cause a choke situation in which the coverage area of the sector shrinks, thereby precluding calls from getting through and possibly prematurely terminating ongoing calls.